This application claims the benefit of Japanese Patent Application Number 2004-4610 filed Jan. 9, 2004, the entirety of which is incorporated by reference.
1. Field of the Invention
The present invention relates to a driver drill usable with a selection of a clutch mode and a drill mode.
2. Description of the Related Art
In a driver drill, firstly, a clutch mode is achieved in a planetary gear reduction mechanism disposed between a motor and a spindle with a structure in which one of internal gears interlocked with the circumference of planetary gears can be rotated within a housing. Also, the internal gear is pressed and locked by a coil spring through steel balls held by a gear case accommodating the planetary gear reduction mechanism and engaged with an end face of the internal gear and through a washer externally provided to the gear case so as to abut on the steel balls. That is, when a load on the spindle is increased to exceed a biasing force of the coil spring, the internal gear idles to interrupt the transfer of rotation to the spindle.
On the other hand, a drill mode is achieved by a locking means that makes a spring holder for holding the coil spring or another pressing member directly abut on the washer disposed between the steel ball and the coil spring by rotative operation of an operating member, such as a change ring, thereby regulating the movement of the washer. However, as tolerances of the components, such as the washer and the pressing member, is increasingly accumulated, the washer might move to operate the clutch even in the drill mode. To solve this problem, in a clutch mechanism disclosed in Japan Published Unexamined Patent Application No. 9-79292, protrusions are provided so as to abut on the outer circumference of the washer and an inner surface of a cap as an operating member. According to this mechanism, when the drill mode is selected, the protrusions of the cap ride on the protrusions of the washer, thereby regulating the movement of the washer without a spring holder.
However, the clutch mechanism disclosed in the above patent document is designed to regulate the movement of the washer externally provided to the housing by using a cap, which is a member separated from the housing. Therefore, even with the clutch mechanism, an influence of the tolerances of the housing and the cap cannot be eliminated. After all, the possibility of the occurrence of erroneous operation of the clutch in the drill mode cannot be prevented.